1. Field of the Invention
The present invention relates to a relief valve device capable of allowing an oil pump of a vehicle engine or the like to discharge oil with an appropriate discharge pressure in low, medium, and high rotation speed ranges of the engine.
2. Description of the Related Art
Conventionally, there are various types of relief valve devices each provided in an oil circulation circuit that supplies oil to an engine and supplying oil with a hydraulic pressure appropriate for low, medium, and high rotation speed ranges of the engine. Japanese Patent Application Publication No. 2010-238205 discloses an example of a relief valve device of this type.
The invention disclosed in Japanese Patent Application Publication No. 2010-238205 will be described briefly. In the following description the reference numerals used in Japanese Patent Application Publication No. 2010-238205 are used as they are by putting the same in brackets. In a valve body (27) which is a relief valve, an orifice-shaped return passage (26E) is formed downstream a back pressure chamber (35) which is a hydraulic pressure control chamber. In a state in which oil is relieved (exhausted) with low hydraulic pressure (see FIGS. 4A and 4B in Japanese Patent Application Publication No. 2010-238205), the oil returns from the back pressure chamber (35) to an intake side of a pump through a return passage (26E) formed in a sleeve (26).
In a state in which oil is relieved (exhausted) with high hydraulic pressure (see FIGS. 5A and 5B in Japanese Patent Application Publication No. 2010-238205), oil cannot move from the back pressure chamber (35) to the return passage (26E) formed in the sleeve (26) and the oil in the back pressure chamber (35) cannot return to the intake side of the pump.